The present invention relates to a single-cylinder circular knitting machine with anti-twist device, in particular for manufacturing socks or stockings.
As is known, single-cylinder circular knitting machines for manufacturing socks or stockings are generally provided with a device termed "anti-twist" which during the manufacture of the product prevents said product from becoming twisted due to the rotation of the needle cylinder about its own axis.
More particularly, the needle cylinder is provided with an axial through cavity which is extended downward by an outer tube. The terminal lower part of said tube is perforated, and a chamber is defined around it; said chamber can be connected to a suction device so as to generate a suction along the cavity of the needle cylinder which subjects the product to tension during its manufacture and makes it adhere to the perforated region of the outer tube. The adhesion of the product to the outer tube, which rotates together with the needle cylinder, avoids the twisting of the product itself and, at the same time, causes an accumulation of the product between the upper end of the needle cylinder and the perforated region which is particularly useful in the case of products having a considerable length, such as for example ladies, stockings.
Furthermore, a coaxial inner tube is arranged in the outer tube and is arranged so that its upper end is at the upper end of the needle cylinder, i.e. proximate to the needle working region. When the manufacture of the product is complete, said inner tube is connected to a suction device and the suction in the outer tube is interrupted so that the product progressively rises along the interspace defined between the outer tube and the inner tube and is automatically extracted from the machine, passing through the inner tube. The transfer from the outside toward the inside of the inner tube, entering from its upper end, also automatically turns the product inside out, as required in order to perform subsequent operations, such as for example the closing of the toe of the product.
Said known types of machine with anti-twist device have some problems.
In fact, in the case of products manufactured with particular types of thread, the raising operation of the sock or stocking along the inner tube can be difficult. In order to avoid this problem, in many cases pressurized air is fed through the perforated region of the outer tube so as to aid the aspiration of the product along the inner tube.
However, this solution entails the use of a more complicated pneumatic circuit, and the pressure of the air fed into the outer tube must be adjusted according to the type of thread used in manufacturing the product. It is furthermore necessary to use relatively high-power suction devices.
Another problem which can be observed in known machines is the difficulty in eliminating any production rejects which arrange themselves between the outer tube and the inner tube. In many cases, the suction applied to the inner tube is sufficient to remove the production reject, whereas in other cases the suction is ineffective, with the problem that the unremoved reject partially or totally closes the holes of the outer tube, causing malfunction of the anti-twist device during the manufacture of successive products. In this case, it is necessary to stop the machine and intervene manually with considerable difficulties, due to the length of the needle cylinder and to the small dimensions of the interspace between the outer tube and the inner tube.
Furthermore, with known machines, when the product does not have to be turned inside out at the end of manufacture, it is necessary to intervene manually in order to remove the inner tube.